One step in the production of aluminum is the smelting of alumina into aluminum metal. The smelting takes place in large, steel, carbon-lined furnaces known as reduction cells. The carbon lining is called a cathode. Alumina is fed into the cells where it is dissolved into molten cryolite (a liquid that can dissolve alumina and conduct electricity at about 970° C.). Carbon block anodes are electrically conductive and are used to introduce electricity into each cell.
The carbon anodes are made in a three-step process. First, petroleum coke and recycled carbon from used anodes are mixed with liquid pitch. This mixture is heated to form a hot paste. The paste is then cooled, and hydraulically pressed or vibrated into a mold to form an anode block. In the second step of the process, the carbon anodes are then “baked” in a carbon baking furnace. This “baking” process helps rid the anodes of impurities and improves their strength and electrical conductivity. Lastly, the carbon anode is then bonded to a metal rod using molten cast iron. This rod allows the anode to be suspended from the reduction cell's super structure during the smelting process.
Perhaps the most important step in forming the carbon anode is the baking process. Precise, uniform heating is necessary to produce a uniform chemical conversion of the raw material to the finished anode block with the desired electrical and physical properties that are required for aluminum smelting. In this respect, the center temperature of the anode is critical and it is important that such temperature be maintained during the heating portion of the “baking” process.
The present invention provides an improved flue wall structure for use in baking carbon anodes in a carbon baking furnace.